1. Field of the Invention
The present invention relates to an image processing method that may be adopted to remove noise contained in an image.
2. Description of Related Art
The noise removal technologies in the related art include noise removal filters referred to as edge-preserving smoothing filters that assure adaptive smoothing with edge structures retained intact by adaptively comparing the size of edges in image structures with the noise fluctuation width. Such edge-preserving smoothing filters include the σ filter disclosed in non-patent reference 1, the bilateral filter disclosed in non-patent reference 2 assuring a higher level of performance and the modified bilateral filter disclosed in patent reference 1 by the inventor of the present invention.
Noise may also be extracted through a simpler noise extraction method such as that disclosed in patent reference 2, whereby the difference between the original image and a uniformly smoothed image is determined and the edge component and the noise component contained in the difference are separated from each other through nonlinear conversion processing, although this method normally does not assure the level of edge/noise separation accuracy of the edge-preserving smoothing filters described above. In a similar technology disclosed in patent reference 3, the difference between an edge-emphasized image (obtained through local filtering processing executed in the actual space) and a uniformly smoothed image is determined, the noise component and the edge component in the difference are separated through nonlinear conversion and the noise component is corrected by using the edge component as an index. In the latter method, the influence of the noise contained in the edge component is minimized by applying a median filter to the edge component for noise removal.    Patent reference 1: International Publication No. 2006/068025 pamphlet    Patent reference 2: Japanese Laid Open Patent Publication No. 2002-74356    Patent reference 3: U.S. Pat. No. 6,055,340    Nonpatent reference 1: J. S. Lee, “Digital Image Smoothing and the Sigma Filter” Computer Vision, Graphics and Image Processing Vol. 24 pp. 255-269, 1983    Nonpatent reference 2: C. Tomasi et al., “Bilateral Filtering for Gray and Color Images” Proceedings of the 1998 IEEE International Conference on Computer Vision, Bombay, India